Because of rapidly escalating energy costs, there has been a steady increase in the use of solar collectors for the purpose of preheating water for domestic and industrial purposes. Numerous preheating systems, which vary in the degree of complexity and practicality, have been proposed. In many of the systems, a heat transfer fluid is circulated through a series of solar collectors in which it is heated by solar energy. The heat transfer fluid is then circulated through a heat exchange system in which the energy from the heat transfer fluid is delivered to a load such as water. The heated water is then used directly, stored for later use, or heated an additional amount by auxiliary heating means.
Most solar heating systems are designed for maximum efficiency, so that they will be relatively effective during most of the daylight hours in all seasons, even in colder climates. Most solar heating systems have provisions for storing the thermal energy during the peak energy gathering periods, so that the energy can be used during periods where little energy is collected. However, since solar systems are geared to function during non-peak periods, excessive heating of the heat transfer fluid sometimes occurs during the peak periods which tends to create problems in the solar system. Excessive heat prevents the use of some materials which might otherwise be used in the solar collectors, because of desirable qualities such as thermo-insulation, lightweight, and cost. The principal disadvantage of excessive heat is the effect that the heat has on the heat transfer fluid itself. Many materials commonly used as heat transfer fluids break down at high temperatures. For example, many types of antifreeze solutions break down at high temperatures and lose their chemical stability. This causes chemical corrosion of many of the components in the entire system. The deterioration of the components comprising a solar collector is also exacerbated by unnecessary exposure to high temperature. Also, replacement of these transfer fluids is expensive. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
One of the most serious problems encountered in solar heater systems is "stagnation". "Stagnation" is defined as a condition in which there is no fluid flow in the system. Some of the causes of stagnation are:
1. a mechanical or electrical failure in the pump, PA1 2. accidental shutting of a valve in the system, PA1 3. failure of a thermo sensor in the system, PA1 4. failure of an automatic control element, PA1 5. shutdown of the solar loop because of a fully charged situation at the heat exchanger or load.
Stagnation may occur for one or more of the above reasons even if the sun is shining. When this occurs, the heat transfer fluid heats up quickly in the collectors beyond the chemical stability of the fluid. The system must then be drained and the fluid replaced. Also, there is some corrosive damage in the system if the condition is not discovered quickly.
It is, therefore, an outstanding object of the invention to provide a solar heater which is provided with a temperature control means for the heat transfer fluid which prevents overheating of the fluid.
Another object of this invention is the provision of a solar heater in which the temperature of the heat transfer fluid is maintained below a preset value at the point where it is utilized for heat exchange with a liquid load.
A further object of the present invention is the provision of a solar heater in which the heat transfer fluid is automatically cooled when it has reached a preset temperature.
It is another object of the instant invention to provide a solar heater in which the flow of the heat transfer fluid through the system is precisely controlled.
Another object of the present invention is to limit the temperature achieved in the solar collectors through the use of the heat-dissipating conduit in a thermosiphoning mode.
A further object of the invention is the provision of a solar heater in which stagnation is prevented.
A still further object of the invention is the provision of a solar heater in which the rate of cooling of the heat transfer fluid is precisely controlled.
It is a further object of the invention to provide a solar heater in which the entire solar heating system is balanced with respect to the flow and temperature of the heat transfer fluid to provide a steady and predictable heat exchange condition at the point where heat is transferred from the heat transfer fluid to the liquid load.
It is still a further object of the present invention to provide a solar heater which is simple in construction, and which is capable of a long life of useful service with a minimum of maintenance.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.